The objective of the proposed research is to examine the relationship between transport processes and cellular metabolism using isolated perfused renal tubules from the rabbit. Standard radioisotopic and microanalytic techniques will be used to measure fluid, glucose and phosphate absorption rates in proximal renal tubules in vitro during simultaneous monitoring of mitochondrial NADH or intracellular pH using microfluorometry or microspectrophotometry of pH sensitive intracellular dyes.